1. Using a sharp knife, cut the carrots into thin sticks.
2. Heat the corn oil in a large preheated wok.
3. Add the onion, carrots, mangetout (snow peas) and baby corn cobs to the wok and stir-fry for 5 minutes.
4. Using a sharp knife, thinly slice the tuna.
5. Add the tuna to the wok and stir-fry for 2-3 minutes, or until the tuna turns opaque.
6. Mix together the fish sauce, palm sugar, orange zest and juice, sherry and cornflour (cornstarch).
7. Pour the mixture over the tuna and vegetables and cook for 2 minutes, or until the juices thicken. Serve with rice or noodles.